These efforts covered both basic and applied aspects of mycoplasmas and related wall-free prokaryotes, including their neurotoxins, antigens, and other biological factors involved in virulence, their immunological interrelationships, and their possible role in human disease(s) of uncertain etiology. Current projects concern the characterization, pathogenicity, and serological properties of an expanding group of helical mycoplasma (spiroplasmas) being isolated from plants and a variety of insects (especially ticks). Experimental infections of suckling rats with a pathogenic spiroplasma (SMCA) has shown a variable occurrence of spongiform encephalopathy and no obvious inflammatory response in brain tissue, despite the appearance of central nervous system symptoms and as many as 108 organisms/gm of brain tissue. Helical spiroplasmas are not observed in brain sections examined by EM. This observation has obvious similarities to a number of "slow virus" infections of the human central nervous system. Culture medium developed in this section for spiroplasma isolation has been successfully employed in the recovery of a new mycoplasma from the human urogenital tract of patients with non-gonoccoccal urethritis. The organism possesses a unique specialized terminal structure that appears to play some role in attachment of the organism to tissue cells.